This invention relates generally to cylinder-type locks having a core, a housing and tumblers which cooperate to define a locking mechanism for the lock. More particularly, the invention relates a high security cylinder lock arrangement which is resistant to conventional lock picking techniques.
Various types of cylinder locks are presently available in the art. Cylinder-type locks are typically comprised of a key plug or core which is rotatably mounted within a cylindrical housing and a locking mechanism which prevents rotation of the core if a correct key is not inserted into the keyway of the lock. The locking mechanisms typically include either tumblers, side bars or a combination of both. Typically, insertion of a key corresponding to the lock (hereinafter "a correct key") raises the tumblers above the shear line which is defined by the outer surface of the core and the inner surface of the housing.
Tumbler type locking mechanisms are typically comprised of a plurality of tumblers, which are reciprocally mounted within aligning bores in the core and housing. The tumblers, which usually comprise cylindrically shaped pins, are typically spring biased across the shear line such that they normally cross the shear line when a correct key is not inserted in the lock. The tumblers thus prevent the core from rotating within the housing when the correct key is not used.
Tumbler locking mechanisms may incorporate tumblers which are each comprised of two separate tumbler parts or segments which have a mating surface at the separation. Each of the tumblers includes a spring biased plug tumbler and a change tumbler. The tumblers are configured such that when the correct key (described in more detail below) is inserted into the keyway, the separation between the plug and change tumblers occurs at the shear line. The plug tumbler is biased radially inwardly into the core such that when the correct key is not inserted into the keyway of the lock, the plug tumbler crosses and blocks the shear line. The tumbler thus prevents the core from rotating in the housing thereby defining a locked position for the lock. When a correct key is inserted into the lock, the key causes the change tumbler to be moved radially outward to a position such that the separation between the plug and the change tumblers occurs at the shear line. This position of the tumblers defines an open or unlocked position for the lock.
The proper or correct key for the lock conventionally includes a plurality of bits or cuts along the top edge of the key, with each of the cuts having a different height. These cuts urge the change tumblers radially outward causing the separation surface of the two tumbler parts to be aligned with the shear line thereby allowing the key plug to be rotated.
These conventional pin tumbler cylinder lock arrangements may be picked by using known lock picking techniques. Typically, in these known techniques, a tool is used to apply pressure to the cylinder core causing relative displacement to occur between the core and the housing. This tensioning movement latches the tumbler pins in the bores of the housing such that they will resist radial movement (movement along the longitudinal axis of the tumblers). That is, when the latching force which results from the tensioning movement exceeds the biasing force of the springs, the tumblers may be moved radially outward and will not be moved back by the spring biasing mechanism. Another tool is then used to raise the cylinder pins across the shear line.
In another lock picking technique, which is commonly referred to as impressioning, a blank key is inserted into the keyway and turned such that an impressioning mark is left to indicate the location of the tumblers. The marks are then used to form a key which will open the lock.
To this end, a number of improved lock arrangements have been developed to help resists these lock picking techniques. These improved lock configurations typically include the use of tumblers arranged in different radial directions, side bars, tumblers with skew-cut bits which cooperate with a skewed cut on the key to rotate the tumblers, and a variety of other configurations.
For example, U.S. Pat. No. 4,434,636 (Prunbauer) discloses a cylinder lock, which in addition to convention pin type tumblers, includes an auxiliary tumbler and a feeler element which cooperate to form an additional locking mechanism. When in the locked position, the upper surface of the auxiliary tumbler engages a cammed arresting recess in the housing to prevent the core from rotating. The feeler element is arranged such that when a correct key is not inserted in the lock, the feeler element urges the auxiliary tumbler outwardly into the arresting recess of the housing. The feeler element includes a recessed section which cooperates with the auxiliary tumbler such that when they are aligned the auxiliary tumbler is permitted to move radially inward. The cammed surface of the housing cams the auxiliary tumbler into the core and out of engagement with the arresting recess when 1) the recessed section of the feeler element is aligned with the auxiliary tumbler and 2) the core is rotated. The feeler element is arranged such that it extends into the keyway. The key includes a recess in one of its sides which cooperates with the feeler element to align the feeler element's recessed section with the auxiliary tumbler.
Another cylinder lock arrangement is disclosed in U.S. Pat. No. 4,723,427 (Oliver). The arrangement disclosed in this patent includes twisting tumblers operated by a bitted key having at least one skew-cut bit. The lock is also provided with a side bar as an additional locking mechanism. The side bar is symmetrically disposed in a plane which passes through the center of the core and which is normal to the plane of the keyway. The cylinder housing includes a slot with a cammed surface which receives the side bar. When in a locked position, the side bar is urged into the slot. The side bar and slot thus cooperate to prevent the core of the lock from rotating.
The side bar includes a plurality of legs which extend into the keyway and abut the outer radial surface of the tumblers when the lock is in the locked position. The side bar is further arranged such that the legs of the side bar intersect not only the outer radial surface of the tumblers but the profile of the key. The tumblers include axial slots which receive the legs of the side bar upon rotation of the tumblers to the correct position. The skew-cut bits in the key function to rotate the tumblers to this correct position. The profile of the key also includes slots which extend normal to its longitudinal axis. When the correct key is inserted into the keyway, the legs of the side bar are aligned with both the slots in the tumblers and the slots in the key thereby allowing the side bar to move radially inward. When the correct key is inserted and the core is rotated, the cammed surface of the slot in the housing urges or cams the side bar radially inward.
Other cylinder lock configurations which include additional sets of tumblers in different radial directions are illustrated in U.S. Pat. Nos. 4,343,166 (Hofmann); 3,802,234 (Gerlach); 3,393,542 (Crepinsek); and 3,181,320 (Bauer).
Although each of the above discussed lock arrangements provides a higher degree of security than is accomplished by using only conventional pin tumblers, they each have unique disadvantages.
For example, if the additional tumblers which are to provide the additional security feature are accessible from the keyway, a person attempting to pick the lock need only use the same techniques to pick the additional tumblers as are used to pick conventional type locks.
In arrangements where (1) an additional tumbler cooperates with a pin-type tumbler to permit the additional tumbler to move into an unlocked position and (2) the additional tumblers include a camming surface which moves them out of the locked position, the person attempting to pick the lock need only to pick the pin-type tumblers and rotate the core to move the lock to the unlocked position. Because of the cammed surface of the additional tumblers, the additional tumblers do not lock the core and housing without the aid of the cooperating pin-type tumblers. Thus, if the cooperating pin-type tumblers are moved to the unlocked position, the additional tumblers will not prevent the core from rotating.
Arrangements using a side bar have the same disadvantages. If the tumblers which hold the side bar in the locked position are moved to the unlocked position, the side bar will not function to prevent the core from rotating because of the cammed surfaces of the side bar and housing.
Further, impressioning techniques may be fairly effective in picking locks which use tumblers that engage only the top edge portion of the key.
Therefore in view of the above, it is a primary object of the present invention to provide a pick resistant high security cylinder lock.
It is a more particular object of the present invention to provide a high security cylinder lock which resists picking by conventional lock picking techniques such as tensioning and impressioning.
It is a further object of the present invention to provide a high security cylinder lock which will remain locked even if the tumblers which are accessible from the keyway are moved to the unlocked position.
It is still a further object of the present invention to provide a pick resist lock which utilizes a key having multiple types of key cuts.